1. Field of the Invention
This invention relates to a process for preparing a device utilizing a semiconductor to be mounted on various electronic instruments, namely a semiconductor device such as a memory, photoelectric converting device, display device, signal processing device, etc.
2. Related Background Art
The main preparation steps of a semiconductor device are the steps of forming a film of a metal, semiconductor, insulator, etc. on a substrate, and finely working the film to a desired pattern.
In recent years, as represented by a semiconductor memory device (memory), larger capacity and higher performances of functions of the device have rapidly advanced and, accompanied therewith, the circuit pattern has become finer and the circuit structure more complicated. On the other hand, a display device such as a liquid crystal display, plasma display, etc. is becoming increasingly larger, and the device function also more complicated. Accordingly, the film forming step and the etching step for performing fine working are steps using a solution or carried out in vacuum and now primarily the so called dry steps by use of plasma or excited gas in reduced pressure gas are used. However, in the photolithographic process generally used for performing a desired fine working, complicated and cumbersome processes such as resist coating, pattern exposure, developing, etching, resist peel off, etc. are employed. Among them, since solutions are employed in the resist coating, developing and resist peel off steps, they cannot be made dry processes. Also, a washing step and drying step after the solution treatment accompanying these steps are required, whereby the steps are increased. Further, since a resist is employed, the resist is peeled off, which increases the generation of dust, whereby deterioration of device performance and lowering of yield will be brought about to increase the cost as a whole.
For example, for formation of Al to be used primarily as the material for the electrode or wiring of the device, there has been employed a method in which Al film is deposited on the whole surface followed by etching to work it into a desired pattern. As the deposition method of Al film, there has been used a sputtering method such as magnetron sputtering in the prior art. Because, generally speaking, the sputtering method is a the physical deposition method based on scattering of the particles sputtered from the target in vacuum, the film thickness at the stepped portion and the insulating film side wall becomes extremely thin, even being broken in an extreme case. Such nonuniform film thickness or breaking is the main cause for markedly lowering the reliability of LSI.
For overcoming the problems as described above, various types of CVD (Chemical Vapor Deposition) methods have been proposed. In these methods, the chemical reaction of the starting gas in some form is utilized in the film forming process. This is caused by the occurrence of decomposition of the starting gas in plasma CVD or optical CVD in the gas phase, and the active species formed there further react on the substrate to effect film formation.
In these CVD methods, the reaction occurs in the gas phase, and therefore surface coverage on the substrate surface is more even as compared with the sputtering method, but carbon atoms contained in the starting gas molecules may be incorporated into the film and also particularly in the plasma CVD, as in the case of the sputtering method, there is damage from charged particles (so called plasma damage).
In the hot CVD method, the film grows primarily through the surface reaction on the substrate surface, and therefore the surface coverage is good even over an unevenness such as a stepped difference on the surface. For this reason, wire breaking at the stepped portion can be avoided. Also, there is no charged particle damage as in plasma CVD or the sputtering method. For this reason, as the method for forming Al film, hot CVD methods have been variously studied.
For example, in the example seen in the Journal of Electrochemical Society Vol. 131, p. 2175 (1984), by use of triisobutyl aluminum {(i-C.sub.4 H.sub.9).sub.3 Al} (TIBA) as the organic aluminum gas, a film with a 3.4 .mu..OMEGA..multidot.cm is formed by film formation under the conditions of a film forming temperature of 260.degree. C. and a reaction tube pressure of 0.5 Torr. When TIBA is employed, no continuous film can be obtained, unless a treatment such as flowing of TiCl.sub.4 to activate the substrate surface and form a nucleus is performed before film formation. Also, including the case of employing TiCl.sub.4, the surface flatness is generally poor when TIBA is employed.
Japanese Laid-Open Patent Application No. 63-33569 discloses a method of forming a film by heating an organic aluminum in the vicinity of the substrate without use of TiCl.sub.4. In this case, the step of removing the naturally oxidized film on the substrate surface is required.
Since TIBA can be used alone, no carrier gas other than TIBA is required to be used, but it is described in the application that Ar gas may be also used as the carrier gas. However, no reaction of TIBA with other gases (e.g. H.sub.2) is contemplated at all. This is because it is difficult to predict what kind of organic metal should be used and how it should be deposited, because the chemical properties of organic metals generally vary greatly when the organic substituent varies even a very little.
In etching of Al, after-corrosion occurs, namely corrosion of aluminum by generation of HCl through the reaction of Cl.sub.2 or the reaction product (AlCl.sub.3, etc.) attached during etching by use of the chlorine type (Cl.sub.2, CCl.sub.4, etc.) gas with a moisture remaining in the air or the etching chamber occurs, thereby causing a great deal of breaking of wiring and electrodes.
On the other hand, separately from these techniques, there is the method of irradiating selectively light onto the substrate surface according to the optical CVD method, thereby causing a photochemical reaction to occur only at the irradiated surface to effect selectively deposition, but it is impossible to completely avoid the occurrence of a reaction in the gas phase, and deposition cannot but occur also at other portions than the irradiated site. Also, the deposition speed of optical CVD method is generally slow, and the deposition speed is smaller by about one power of 10 as compared with the hot CVD method.
Thus, as described above, in the steps of the prior art, there remains much room for improvement corresponding to further higher integration and performances of semiconductor devices.